


the first bite

by erythea



Category: Fate/Grand Order
Genre: M/M, Moriarty won't shut up about math, One-Sided Attraction, Victorian Repression, i probably got the math wrong but don't worry about it, not so much of a corruption as it is a downward spiral, set during the short story about Jekyll and Hyde from Watson's perspective
Language: English
Status: Completed
Published: 2020-11-20
Updated: 2020-11-20
Packaged: 2021-03-09 23:41:59
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 4,375
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/27644285
Author URL: https://archiveofourown.org/users/erythea/pseuds/erythea
Summary: “What do you think?” Jekyll beamed, eyes shining and expectant.“To say I underestimated you would hold the unfortunate implication that I found your abilities lacking,” Holmes replied. “If I was looking for another assistant, all other things constant, you might be my first choice.”“Could I?” Jekyll asked without missing a beat. “I mean, I could never! Mr. Sherlock Holmes and Dr. John Watson — the two names are perfectly inseparable.”“I can’t argue with that,” Holmes admitted, his smile winsome and his chin raised high, but as he turned away to smoke his pipe, Jekyll saw the corners of his mouth drop. “Don't get ahead of yourself, Jekyll. I never said I wanted you to do this.”Jekyll admires a certain detective a little too much. Moriarty notices.
Relationships: James Moriarty | Archer/Jekyll and Hyde | Assassin and Berserker, Jekyll | Assassin/Sherlock Holmes | Ruler
Comments: 2
Kudos: 16





	1. Chapter 1

**Author's Note:**

  * For [poludeuces](https://archiveofourown.org/users/poludeuces/gifts).



> Commission for Adet! He wanted a fic about Moriarty seducing Jekyll with some one-sided Holmes/Jekyll. Jekyll's a goddamn mess, but we all love him here.

Henry Jekyll’s shoes clicked against the pavement as he eagerly left the university one spring afternoon. He wasn’t quite satisfied with his lectures, but he wasn’t that disappointed with them either, which was a strange thought for him to have. Jekyll had been having a number of strange thoughts lately. It was a given that he did sometimes worry about whether his work would go well, but he never once considered how his work made him feel. He ought to feel good. He should be feeling good after the fact, but his present mood had nothing to do with his day job. Jekyll was free for the rest of the afternoon.

An afternoon he would devote to the renowned detective, Sherlock Holmes.

It could be said that death and pestilence were two of the greatest evils on this earth, but Dr. Henry Jekyll saw them as a part of nature — inevitable. What was truly vile was the temptation of the Devil. This evil, invisible creature spurred others to commit acts in the name of pride, lust, anger and greed — sins only humans were capable of. And the more Jekyll peered into the shadows of society, the more it appeared to him that this serpent was not too different from humanity itself.

Jekyll did not want to believe this.

But supposing it were true, there were still people who overcame this truth.

Sherlock Holmes was one of them.

Assisting Sherlock Holmes made Jekyll’s chest swell with pride. Men like Henry Jekyll contributed to the world with their ability to save lives and change nations, but it was men like Sherlock Holmes that moved the hearts of adults and children alike. The detective solved crimes and sought justice for the good of all, triumphing over evil. And for his triumph, Jekyll was honored to play his part.

It was with these thoughts that Jekyll walked down the otherwise gloomy streets of London with a spring in his step. Every piece of information he could give Holmes was a good deed, and every good deed was one step further for one of the greatest heroes of the century. Sherlock Holmes would never call himself that, but Henry Jekyll’s eyes were clear of all doubt. The sooner he could get back to work — thrilling, more fulfilling work — the sooner he could help the man he admired.

_ Wait _ , he thought.

Thrilling?

What an odd choice of words. He wasn’t helping the detective because it was  _ fun. _

But he can’t deny how he faltered when an acquaintance interrupted his otherwise pleasant journey.

“Dr. Henry Jekyll! What a coincidence.”

It was Professor James Moriarty, who approached him in swift strides. He was a charismatic, distinguished gentleman in his fifties, smartly and appropriately dressed for his position and reputation. In the field of mathematics, there was no one who was more capable and renowned in the current era than Professor Moriarty. In academic circles, Jekyll had run into the professor enough times to remember his face, but he didn’t think the man would remember his name.

Sherlock Holmes wasn’t rushing Jekyll for his investigations, but in contrast to his eagerness to work for the detective, Jekyll was marginally less enthusiastic about running into Moriarty. The professor was not bad company. He just wasn’t Mr. Holmes. Perhaps if Moriarty knew martial arts, or used his intellectual and (nonexistent) physical prowess to mete out justice, he would hold Jekyll’s attention — not that Dr. Henry Jekyll was a strong proponent of violence, of course. Alas, it seemed that while Moriarty cared for the public good, he had the same power and attitude as any normal citizen would. Among all the men in London, truly, Sherlock Holmes was a cut above them all.

So Jekyll greeted the professor as he did any colleague: with a genial smile.

“Good afternoon, Professor Moriarty. What brings you here?”

“Oh, business. And by business, I mean I have an appointment with my physician. One must take great pains to maintain their youth, especially one as young as I.” Moriarty adjusted his lapels. “But seeing as we’re both noble, humble scholars dedicated to our pursuit of knowledge, Henry, I should hope I haven’t given you the opportunity to misconstrue my intentions. Why, we are men in the proximity of an institution of learning, far too learned to risk undermining its institutionality! Turning into idle profligates should be the last thing on our minds.”

Jekyll didn’t know when he started being on a first-name basis with Professor Moriarty, but he didn’t mind, so he paid it no mind.

“I agree. Rest assured you’ve given me no ideas at all, Professor. Um, I should be worried if you did.”

“Indeed, you should,” Moriarty replied. “And Moriarty will do just as fine. You’re not my student! There’s no need for you to call me professor, is there?”

“Oh! Yes, I’m aware, but I really must insist.”

They both continued to walk along the pavement.

“No, I was just pleasantly surprised to see you here. Yes, I was surprised to see you outside the library, or your study, or anywhere indoors at all. All work and no play makes Jack a very dull boy! It would make him almost as dull as a Charles who doesn’t care for calculus.”

“The outdoors have their merits,” Jekyll said brightly, “but I like the indoors. There are less distractions. They provide boundaries.”

“Boundaries, boundaries, yes,” Moriarty replied. “Understanding limits are quite important in piecing things together and taking them apart. Again, I speak of calculus — the study of change. I know what you want to say, Henry. ‘The same could be said of chemistry!’ That’s one aspect of it, I suppose. But chemistry specifically talks of elements and substances, all which exist on the physical plane. Calculus, no, all mathematics takes place in a more perfect space. Rather, it is that which holds all sciences together!”

“I doubt I’d be able to practice without it,” Jekyll admitted, for he knew it was the only thing he could say in reply.

“Precisely. It has many applications. That is the beauty of maths. We can apply it to even the simplest of conundrums. Where are you headed now, Doctor?”

“I’m off to help a friend. I’m sorry to say that divulging anything more will put him in greater peril, so I must leave it at that. He’s a very dear friend of mine.” Jekyll paused and out of nervous habit, pushed his glasses up the bridge of his nose. “Well, that is what I hope for.”

“Oh?” Moriarty’s smile grew wider as he lowered his voice conspiratorially. “My, my, Dr. Jekyll. The uncertainty in your voice is most intriguing. While private relations are no interest of mine as a professor, as a nosy colleague, they rouse my curiosity. Tell me more! I must know the details at once.”

Jekyll walked faster. “I haven’t the faintest idea what you’re talking about.”

Moriarty picked up the pace. “Henry? No, Harry! Don’t be like that, Harry. Once you reach a certain age, your hair begins to gray and life begins to plateau. Few things excite me anymore. Not even my students want to tell me about their love lives, which they claim to be perfectly nonexistent! I respect their privacy, but can’t they spare some sympathy for little old me? All this man wants is a little stimulation!”

“Please refrain from using the word ‘stimulation’, Professor. It’s very inappropriate.”

“For heaven’s sake, you’re blushing. This acquaintance must be an interesting chap. Oh, what a lucky fellow! I should extremely like to meet him.”

Jekyll held back a sigh. “I'm sure he'd feel the same,” he said, but only for the sake of moving on. “May we return to the topic?”

“Right. As a man who has yet to reach the age of fifty—” (At this, Jekyll pursed his lips.) “—this news delights me. But as a gentleman of good society, I must be reasonable. As I see it, your ability to think is inversely proportional to your desire for your friend.”

“Pardon me, Professor,” Jekyll interrupted, “but it seems you skipped a number of words between ‘desire’ and ‘friend’.”

“I omitted unnecessary details in the interest of time,” Moriarty explained. “Anyway, imagine a graph for the equation y = 1/x. Let the x-axis represent the lengths you must hypothetically go to have this person, and let the y-axis represent your intelligence and sanity.”

Jekyll opened his mouth to protest, but Moriarty carried on.

“In the first quadrant, the graph should form a shape like this.” Moriarty drew a curve in the air that swept to the right. “As X approaches zero, Y increases. However! As X approaches infinity, Y decreases. In other words, the longer you follow this man, the more you’ll fill your brain with nonsense.”

He then rapped his cane against the pavement.

“So don’t be a fool! It doesn’t matter how much he earns or how many properties he has. You may marry when you are thirty-five! That is the advice I always give my students.”

“That explains so many things,” said Jekyll, still recovering from the jolt Moriarty’s antics gave him. “Besides, I’m already past thirty. I honestly can’t tell if you’re encouraging me, Professor. You were very enthusiastic a moment ago.”

“I don’t remember you asking me to stimulate anything. You expressly told me not to stimulate you.”

“That is absolutely not what I said. With all due respect, Professor Moriarty, I can’t help but feel that you just like to be contrary.”

“It is the young rebel in me. In any case, Harry, what you’re playing is a most dangerous game — a game whose results even mathematics cannot account for. I urge you to take care. To desire is human, but how much can one desire until he is called a beast?”

Jekyll peered at Moriarty’s face, searching for the meaning behind his smile. “We’re still speaking of amorous intentions, surely?”

Moriarty raised his hands and stepped aside. “Your words, not mine.”

Jekyll’s face was as red as a beet. “Professor!”

Moriarty laughed once more, and they both ambled down the pavement as they continued to speak of nothing. The professor was having fun, it was clear. With what, Jekyll wasn’t sure. Whatever it was, his heart felt a twinge of envy.

“Oh, dear me!” Moriarty cried as he checked his pocket watch. “This sprightly young gentleman lost track of time and now he is late for his appointment! It is with a heavy heart that I must leave you, Dr. Jekyll. I hope I didn’t keep you for too long.”

“No, not at all,” Jekyll reassured him. “Good day, Professor Moriarty. It was a pleasure.”

“Yes, yes. Stimulating.” Moriarty shook his hand. “It was delightful to see a friend outside his comfort zone. Perfectly wonderful.”

At the time, Jekyll didn’t know what that meant. By the time Moriarty left, he realized the sun had already begun to sink into the horizon.

His investigations would have to wait.

All throughout his childhood Henry Jekyll was an obedient son, but these days, his friends found that hard to believe.

Even the warnings of the detective’s assistant, Dr. John Watson, well-intentioned as they were, did little to dissuade Jekyll from assisting Sherlock Holmes in his investigations. From petty crimes to class-A felonies, he looked into every case and found the information Holmes needed, and he was very good at it. Very enthusiastic, too. He had to be. As far as Jekyll was concerned, he was doing nothing wrong. What reason did Dr. Watson have to convince him otherwise? Jealousy? Fame? Frantic hands ruffled his hair until he looked nothing like the scholar they called him.

Holmes and Watson were already perfect. Did they want perfection from him, too?

_ Good work today, Doctor. Congratulations, Doctor. You’re too kind, Doctor. _

Faceless voices echoed in Jekyll’s mind, mocking him with words that have begun to lose meaning. To survive in Holmes’ world, goodness wasn’t enough. What did Holmes want? What did Jekyll  _ need? _ He whined and groaned, teeth grinding and temples aching as he tried to calm down and think.

He needed peace.

He needed—

He thought about the detective, from his fair face to his flesh and bones. He thought about his lips. He thought about taking them. He thought about how badly he wanted to deserve it.

_ There, there, Doctor. You’re so good to me, Doctor. Will you do that again, Doctor? _

He shoved his papers off his desk, held his head, and shouted with his whole chest, but he did not curse.

He could never curse, for gentlemen should never curse too much at anyone, most of all at themselves. To do so was a very strange thing.

And he just had a very strange thought.

He’s been having many strange thoughts lately.

“If I may, Mr. Holmes,” said Jekyll, who had grown accustomed to the sound on his tongue and his shoes on this floor.

For a while it seemed that he’d stopped contacting the detective for good, but it was only to prepare himself for whatever encounters lay ahead of them. Some cases under Sherlock Holmes were far more frightening than he’d imagined, soaked in the blood and grime of the city’s underworld, and he wasn’t looking forward to seeing where his investigations would lead him. After all, his assistance to Sherlock Holmes was for the good of society and not for any personal gain. It would be utterly foolish to throw himself into something that would damn him to hell.

But something about it intrigued him.

Hell.

The word crossed his mind more often than it should.

And today, he was going to show Holmes how deep it ran.

“If I may, Mr. Holmes, it appears to me that all these cases in the area share some uncanny similarities…”

Jekyll wound lines of string around pins across the map on the board, each point accompanied by a picture or news article. He reported his findings in a concise and methodical manner, and while he never dared to field it, his own theory was clear: there was someone pulling the strings behind all crimes in London.

He was sure Holmes had already arrived at a similar conclusion. When the detective was always ten steps ahead, the doctor made sure he wasn’t too far behind.

“What do you think?” Jekyll beamed, eyes shining and expectant.

“To say I underestimated you would hold the unfortunate implication that I found your abilities lacking,” Holmes replied. “If I was looking for another assistant, all other things constant, you might be my first choice.”

“Could I?” Jekyll asked without missing a beat. “I mean, I could never! Mr. Sherlock Holmes and Dr. John Watson — the two names are perfectly inseparable.”

“I can’t argue with that,” Holmes admitted, his smile winsome and his chin raised high, but as he turned away to smoke his pipe, Jekyll saw the corners of his mouth drop. “Don't get ahead of yourself, Jekyll. I never said I wanted you to do this.”

“But  _ I _ want to do this,” Jekyll insisted. He circled around Holmes and placed himself in front of the detective, gazing upon him with an intensity neither of them knew he was capable of.

“I fear there’s a greater evil among us, Mr. Holmes. As anger and resentment grow within humanity, so does their reason for restraint. It would be one thing if these were isolated cases of violence, but someone out there is exploiting their weaknesses, the gaps in their judgement. We try — I should like to believe we all do — but not everyone can fight it. To know that there might be one singular force behind this… one that knows no limits, one who can crawl into another’s heart and change its colors, spreading its evil like a cancer… I believe that is the most frightening enemy of all. I want to help you catch him.”

As Holmes took a drag from his pipe, the wisps of smoke a stark contrast to his sharp gaze and aquiline nose, Jekyll heard his heart thump loudly in his ears and prayed.

“It’s natural to fear the unknown,” Holmes began.

“Quite so. And that is why I intend to see these cases to the end—”

“Dr. Jekyll, I’m afraid we must stop meeting.”

The doctor’s lips parted.

Then, his heart sank.

“I’m sure Watson has said something to a similar effect,” the detective continued, “but whatever he’s told you is that of his own concoction, and whatever he’s done is that of his own volition. The doctor is his own person. As are you.”

Jekyll opened his mouth, but the answer stuck to his throat. He laughed.

“I don’t understand. Have I failed you at some point? You know I do my best to make up for my shortcomings. I’ll work very hard.”

“It’s not about the quality of your work. I simply can’t allow you to investigate this any further. There are too many unknown variables.”

“You sound like Professor Moriarty,” Jekyll murmured.

Holmes furrowed his brow. “I see you’ve been in touch.”

“If the variables worry you, then we’ll solve for them. Can’t I do that with you?”

It took all of Jekyll’s power to stop the fear from spilling out of his mouth.

“I’m not as ignorant or weak as you think, I assure you. For you— For _ this,  _ I’m willing to do anything! This villain, this Napoleon of Crime is out there—”

“This isn’t a game you can play on a Saturday afternoon, Dr. Jekyll,” came the detective’s terse reply. “I was under the impression that you had a little more than a passing interest in it, but it appears that I was wrong. A man willing to throw his life away for a dream is nothing but a fool.”

Jekyll bit his lip. Henry Jekyll can be a fool, but Sherlock Holmes was never wrong. And if he was, it wouldn’t be about Jekyll.

“Surely you don’t intend to work alone,” said Jekyll, the words trembling in his throat.

“I do what I must,” said Holmes, solemn and certain.

“But Mr. Holmes—”

“I have no need for a liability. I’m truly grateful for all the help you’ve given me, but this is the end of our transaction.”

Transaction.

Liability.

Jekyll’s heart buried itself into his chest until his face was stone cold. There was no need to show him his wounds. Sherlock Holmes was a rational man. Surely this, too, was calculated. He never made a serious decision without a reason.

But Jekyll just couldn’t understand it.

How Holmes could cut him like a knife.

How Jekyll could let him do it.

“Live on, Jekyll. That’s what the money's for, isn’t it?”

“I won’t stay any longer, then. Sorry to bother you.”

It was the last Holmes ever saw of him.

As Jekyll left the apartment complex, Holmes wondered if the doctor himself noticed it — the smile on his face, the glint in his eye, the joy in his voice as he spoke of the dangerous game spiders played with their threads and teeth. 

The problem was this: Henry Jekyll wasn’t good enough.

Thus, the solution was a matter of subtraction.

He left his teaching position at the university, moved residences, and began to cooperate with the Clock Tower. Then, he began to work. Soon, he found the solution to all of humanity’s problems: a drug that could separate good from evil.

The red potion swirled in its vial, as thin as water and clearer than blood, and as he sat alone in his room, Jekyll wondered if this was all worth it. It should be. If not, then what was this all for?

Pride?

Love?

As he opened the vial and held it to his lips, he closed his eyes and made a decision.

For good to triumph, nothing else should matter.

But Jekyll shouldn’t kid himself.

  
  
  


It happened one autumn morning.

Jekyll felt the dates blur into each other as he toiled in his apartment, the days long and the nights even longer. Strange, though, how he never felt too sluggish. He did however tend to wake up with the most dreadful headaches. He’d still be wearing clothes from the night before, which would often smell of alcohol — a habit he feared he’d picked up from all those stressful evenings. By nightfall, he had too much energy to squander. For Jekyll, this was an unfortunate thing, especially during his experiment. There was no telling what would happen if he couldn't control this one variable.  Holmes would certainly have something to say about it.

Today, Jekyll chose to tire himself out and spend his energy in a more productive manner.

He had just come back from a quick errand when the voice of a familiar professor broke the silence in the room.

“Less distractions indoors, are there?”

Professor Moriarty rose from Jekyll’s desk, his cane occasionally clacking against the floor as he moved to greet him.

Jekyll stepped back.

“I have to say it’s a shame to see you here so early, Dr. Jekyll. Especially when the weather is so pleasant.”

“Professor Moriarty. How did you get here? Mr. Poole didn’t inform me—”

“Mr. Poole is free for the day. That’s what you told him yesterday, didn’t you?”

Jekyll took a long pause. “Yes, that’s correct, I think.”

There have been gaps in his memories. He told himself to write them all in his diary to see where the gaps ended and began, but he tended to forget.

He’s been forgetting a lot of things lately.

“As for how I got here, you gave me a key.” Moriarty glanced to his right. “I see you’re interested in reaching for the dagger on your bookshelf. ”

_ How did he— _ “I assure you I have no such intention.”

Moriarty laughed as he leaned back against the desk. “Of course, of course! It is a nervous habit. I noticed.”

“Why are you here, Professor?”

“I was just worried you’d hurt yourself, Harry. You don’t need to be a maths professor to know that.”

“Hurt myself?” Jekyll knitted his brows. “I’m confused. I haven’t told anyone about this place.”

“I’m sure you just forgot. I’m honored that you’d trust me with this at all! I do so love secrets. Have you told your friend about your new address?”

“Friend?” Jekyll rubbed his arm and looked away. “No. I won’t be seeing him anymore, unfortunately. I can’t see him.” His voice fell to a whisper. “Not like this.”

Moriarty’s eyes softened as he clicked his tongue. “Oh, Harry.”

The concern on Moriarty’s face touched Jekyll in a way he never thought he’d feel. Not for the man he’s become. These nights, he didn’t know where he went or what he did, and part of him wished he could stay in the dark.

But on a day like this, Moriarty’s presence seemed to shine brighter than the sun. It drew him closer.

“I did my best to help him, Professor. But I’m— I’m not good enough. Not to protect him. Not to stay by his side.”

“Well, that’s all a matter of perspective, isn’t it? For the graph y = 1/x, the further you traverse along the x-axis, the closer you get to it. And I certainly think you haven’t been travelling along that axis far enough!”

Jekyll squinted through the formula. “But I thought you didn’t want me to want him. You thought I’d lose my mind.”

“Oh, that’s your choice, Harry. I’m not your father, and I’m certainly not a man you should trust.”

“There’s no point either way. I’m a failure. I’ve tried so hard to prove myself, to be everything he needed…” Jekyll hugged himself, hated himself. “In the end, all my efforts were in vain.”

“You know that’s not true.”

“Professor…?”

Moriarty lifted Jekyll’s chin with a finger, and Jekyll stood so closely, he held the table for purchase as he swallowed and feared Moriarty could hear the sound of his heart.

“You’re so full of potential, Harry. You have a wonderful mind, a beautiful soul...”

His gloved thumb ran over Jekyll’s lip, his voice soft and low in his chest.

“Doesn’t it tire you?”

“I don’t know what you mean,” Jekyll gasped, fever rising.

“You really don’t have to hold back, you know. Whatever flaws you think you have, I think they’re perfectly wonderful.”

Jekyll tore his gaze away, but the rest of his body remained, basking and melting in praise he’s never heard. “We can’t do this, Professor. This is wrong, and I could hurt you, and you’re—”

“What?” Moriarty smirked, his eyes shining in the shadows. “You don’t think I can take it?”

Jekyll’s eyes widened at the words, the feeling all too familiar and painful to bear. He grasped the older man’s wrist. “No, I didn’t mean to…”

Moriarty laughed. “Then make your move, Harry. If you walk away now, I won’t stop you. You know how that must feel, I’m sure.”

Jekyll’s heart stopped.

Then, he saw red.

He bared his fangs, shed his skin—

“Don’t look down on me.”

—and like Adam and Eve before him, took his first bite.

**Notes for the Chapter:**

> I thought this would be a good place to end it, but if you're interested in the very short epilogue, that's in the next chapter.


	2. Epilogue

**Notes for the Chapter:**

> Decided to leave this out of the main story because it was too anti-climactic and maybe confusing? But I like it enough to put here.

“Feeling better?”

“I feel bloody brilliant, that’s what.” The man no longer known as Henry Jekyll gave Moriarty a toothy grin. “Beats being the teacher’s pet, yeah?”

“Don’t be like that, Edward. Harry is perfectly charming. And by charming, I mean—”

“Yeah, yeah, adorable bugger, ain’t he? Doesn’t matter. I’m the one you want in bed.”

Edward Hyde laughed as he pushed himself off Moriarty and ambled over to the bookshelf. He grabbed the knife, twirled it in the air, and tucked it hidden into his shirt.

“Soooo… Are you and me leaving or are you gonna sit there like the widow of Windsor?”

Moriarty pushed himself off the desk and strode toward him with newfound vitality. “My dear Edward, the day’s just begun! Let’s have some fun first, shall we? What do you want to do next?”

Hyde brought Moriarty’s hips to his as he murmured into his neck, “Well, we could always go for another round…”

“So full of energy,” Moriarty sighed as he loosened his tie.

Hyde cackled. “You’re so good to me, Professor.”


End file.
